1. Field of the Invention
The present invention relates generally to a zoom projection lens, and more particularly to a zoom projection lens for a projector.
2. Description of the Related Art
In recent days, cathode ray tube (CRT) is replaced by liquid crystal display (LCD), digital light processing (DLP), and other lighter and thinner projecting devices.
In a DLP, chief ray of a non-telecentric system is not parallel to an optical axis so that a zoom lens of the non-telecentric system has one less total reflection prism than a zoom lens of a telecentric system to reduce the cost. Besides, because the chief ray of the non-telecentric system is not parallel to the optical axis, the chief ray enter the zoom lens with a predetermined angle that will make the image projected on the screen shifting upward to meet the requirement of above front projector.
A conventional non-telecentric front projector, which is taught in Taiwan patent 1288290, uses high pressure mercury lamps. Because of the cost, it usually has a small aperture stop, and large F-number, typically is greater than 2.4.
As the improvement of various light sources, more and more manufacturers concern about how to provide a zoom projection lens which may use different light sources and keep a high light efficiency.